Some scientific hypotheses seem too perfect to be anything but true. Long before we understood the processes behind plate tectonics, the natural fit between the coasts of Africa and South America made the notion of their original linkage seem obvious. Although dismissed in many quarters as mere coincidence, the piecing together of earlier continents would follow. The hypothesis of continental movement, whatever the cause, was almost too obvious not to be true.
But does science really work so neatly? Writing about his work on the evident ‘dinosaur killer’ event at the Cretaceous/Tertiary boundary, Walter Alvarez once said:
“Much of the work we do as scientists involves filling in the details about matters that are basically understood already, or applying standard techniques to new specific cases. But occasionally there is a question that offers an opportunity for a really major discovery.”
And the K/T impact seemed, like the continental coastlines, to be an obvious fit, a breakthrough that changed everything.
But the theory of the 65 million year old killer impactor at Chicxulub is again being challenged, at least in terms of its effect on the dinosaurs and the destruction of countless species. Gerta Keller (Princeton University) and Thierry Adatte (University of Lausanne) believe the Chicxulub crater in northern Yucatan was formed some 300,000 years before the mass extinction occurred. Moreover, Keller argues in the upcoming Journal of the Geological Society that not a single species went extinct as a result of the impact.
The debate over Chicxulub is not new. In fact, The Geological Society held an online forum called the Great Chicxulub Debate back in 2004, allowing Keller to argue the case against a single impactor as dinosaur killer:
The Chicxulub impact was not the only thing making life horrible at the end of the Cretaceous. The mass extinction coincides in time with yet another – probably larger – impact right at the Cretaceous-Tertiary (K/T) boundary, which is well documented by virtue of its global iridium distribution. Moreover, massive volcanism that would one day create India’s Deccan traps began during the late Maastrichtian and continued into the early Tertiary 4.5, causing major climate changes and long-term biotic stress. This stress, we believe, culminated in the K/T mass extinction – which we think was the combined effect of both volcanism and impacts.
Image: Sediments show that the Chicxulub meteorite predates a mass extinction 65 million years ago. Credit: Gerta Keller (Princeton University).
The online debate is worth reading, as it lays out the basics of the case, which in its latest findings focuses on sediments deposited during the tens of thousands of years after the impact. Between four and nine meters of sediments, in Keller’s words, “…deposited at about two to three centimeters per thousand years after the impact. The mass extinction level can be seen in the sediments above this interval.”
This sandstone deposition accumulated over a long period and shows all the characteristics of normal sedimentation. That, Keller argues, makes it unlikely that disturbances caused by the impact could have made these deposits unreliable evidence, as some supporters of the Chicxulub impact theory have argued.
If we begin to see the K/T event as the result of more than a single impact at Chicxulub — and perhaps not related to Chicxulub at all — then we are tracing climatic and geological changes that worked in conjunction with a devastating impact elsewhere. In either case, the tale of mass extinctions the Earth tells reminds us that we live in an environment that can turn on its inhabitants. A space-based species backup plan — beginning with asteroid deflection technologies — continues to make long-term sense.
Addendum: A paper by James Fassett in Palaeontologia Electronica, just published today, argues that dinosaurs may have survived in a remote area of what is now New Mexico and Colorado for up to half a million years after the extinction event.
Comments on this entry are closed.
The reason why this is believable to me is because, if a similar sized asteroid or comet hit the Earth today, I think we could easily survive it, assuming you are not near the impact point. If the hit was in the ocean, of course there would be a huge tsunami, which would wipe out the coastal areas of the ocean the impact occurred in. However, the intensity of that tsunami decreases 1/r with distance. People not near that particular ocean would be relatively unaffected.
A land impact would be even easier to survive. Yes, lots of junk would get thrown up in the air (just like when St. Helen’s blew and we got covered in ash) and that debris would stay there for a month or two. As long as you have enough food stored up, you come out the other end and can grow food again when the skies clear. So, your talking about the loss of one season worth of agriculture. The next few years would produce bumper crops, again just like after St. Helens when the wheat and alfalfa yields were so high we didn’t know what to do with it. The rest of the techno-industrial infrastructure (assuming you are not near ground zero) would remain intact. Your electricity, water, internet, and cable TV would be OK (you could watch “Terminator” reruns while waiting for the skies to clear).
Of course if something real big (say 30-100 kilometers in diameter) hit the Earth, then we are all dead. However, scientists assure us that such large objects have not whacked the Earth since the Hadean period (an appropriate name). So, I don’t think we have to worry about this.
I just finished reading “Century Rain” last week Paul, one of Reynolds’ best in my estimation.
You won’t be disappointed.
As for the asteroid, I’ll reserve judgement. I believe I’ve heard of the gap between the asteroid strike and the die-off before, but I’ll have to look it up.
The Deccan Traps were mentioned also.
I like all 4 of Reynold’s “Revelation Space” novels. However, I was disappointed in “Century Rain”. I also found his other stand alone novel “Pushing Ice” to be disappointing as well.
Whether or not Chicxulub is the astrobleme in question isn’t the point. The iridium at the K/T boundary layer is without doubt extraterrestrial in origin.
The Dino Docs on the Dinosaur Mailing List are saying that it’s the same claim, by the same researcher, just rehashed from the last time they put it out. I think in probabilistic terms it’s a very rare thing for an extinction and a major impact event to occur close together in geological time if the two weren’t related. That the extinction itself was a protracted affair might be what the data is really telling us.
I’ve heard the Deccan Traps specter raised before, and it started me wondering: could there possibly be a causal connection between Chicxulub and the subsequent volcanism? I’ve looked on the little maplets of Cretaceous land distribution floating around the internet, and it seems to me that the Indian plate is just about opposite of what would become the Yucatan; but the detail on these tiny maps is so sketchy, and the identification of landmasses so questionable, that this is little better than guesswork. Could someone with access to more accurate paleogeographic data answer this question:
Were the Deccan Traps located on the exact antipodes of the Chicxulub impact, 65 Mya?
Off the top of my head, with no info at hand:
I recall some speculation that the largest extinction event ever (at the beginning of the Age of Dinosaurs) might have been triggered by an impactor that also caused massive volcanism.
Guess I’ll do some web surfing to find out more about that, and about James Fassett. First time I’ve read about dinosaurs surviving the Cretaceous (outside of sci-fi anyway).
A quick glance around the web suggests that Fassett is regarded as a bit of a crank and that the consensus expert view is that no dinosaurs (other than birds) survived the Cretaceous. The alleged Paleocene dinosaurs are generally dismissed as the result of re-working (fossils being moved from their original strata to younger layers) or incorrect dating.
Just summarizing what I read — no firm opinion of my own yet!
Dinos extinction may be due Asteroid crash in India
A massive asteroid crashing off the western coast of India, creating the planet’s largest known crater 40 km across, may have obliterated dinosaurs 65 million years ago, an Indian American has found.
Most of the crater lies submerged on India’s continental shelf, in the area known as Bombay High. The impact appears to have sheared or destroyed much of the 48 km-thick granite layer in the western coast of India.
Mr Sankar Chatterjee of Texas Tech University and his team took a close look at the massive Shiva basin, a submerged depression west of India that is intensely mined for its oil and natural gas. Some complex craters are among the most productive hydrocarbon sites on the planet.
“If we are right, this is the largest crater known on our planet,” Mr Chatterjee said. “A bolide of this size, perhaps 40 km in diameter, creates its own tectonics.”
In contrast, the object that struck Mexico’s Yucatan Peninsula, and is commonly thought to have killed the dinosaurs, was between eight and 10 km wide.
Full article here: